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git.gir.st - tmk_keyboard.git/blob - tmk_core/tool/mbed/mbed-sdk/libraries/dsp/cmsis_dsp/StatisticsFunctions/arm_std_q15.c
1 /* ----------------------------------------------------------------------
2 * Copyright (C) 2010-2013 ARM Limited. All rights reserved.
4 * $Date: 17. January 2013
7 * Project: CMSIS DSP Library
10 * Description: Standard deviation of an array of Q15 type.
12 * Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
14 * Redistribution and use in source and binary forms, with or without
15 * modification, are permitted provided that the following conditions
17 * - Redistributions of source code must retain the above copyright
18 * notice, this list of conditions and the following disclaimer.
19 * - Redistributions in binary form must reproduce the above copyright
20 * notice, this list of conditions and the following disclaimer in
21 * the documentation and/or other materials provided with the
23 * - Neither the name of ARM LIMITED nor the names of its contributors
24 * may be used to endorse or promote products derived from this
25 * software without specific prior written permission.
27 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
28 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
29 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
30 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
31 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
32 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
33 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
34 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
35 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
36 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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38 * POSSIBILITY OF SUCH DAMAGE.
39 * -------------------------------------------------------------------- */
53 * @brief Standard deviation of the elements of a Q15 vector.
54 * @param[in] *pSrc points to the input vector
55 * @param[in] blockSize length of the input vector
56 * @param[out] *pResult standard deviation value returned here
60 * <b>Scaling and Overflow Behavior:</b>
63 * The function is implemented using a 64-bit internal accumulator.
64 * The input is represented in 1.15 format.
65 * Intermediate multiplication yields a 2.30 format, and this
66 * result is added without saturation to a 64-bit accumulator in 34.30 format.
67 * With 33 guard bits in the accumulator, there is no risk of overflow, and the
68 * full precision of the intermediate multiplication is preserved.
69 * Finally, the 34.30 result is truncated to 34.15 format by discarding the lower
70 * 15 bits, and then saturated to yield a result in 1.15 format.
78 q31_t sum
= 0; /* Accumulator */
79 q31_t meanOfSquares
, squareOfMean
; /* square of mean and mean of square */
80 q15_t mean
; /* mean */
81 uint32_t blkCnt
; /* loop counter */
82 q15_t t
; /* Temporary variable */
83 q63_t sumOfSquares
= 0; /* Accumulator */
85 #ifndef ARM_MATH_CM0_FAMILY
87 /* Run the below code for Cortex-M4 and Cortex-M3 */
89 q31_t in
; /* input value */
90 q15_t in1
; /* input value */
93 blkCnt
= blockSize
>> 2u;
95 /* First part of the processing with loop unrolling. Compute 4 outputs at a time.
96 ** a second loop below computes the remaining 1 to 3 samples. */
99 /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
100 /* Compute Sum of squares of the input samples
101 * and then store the result in a temporary variable, sum. */
102 in
= *__SIMD32(pSrc
)++;
103 sum
+= ((in
<< 16) >> 16);
105 sumOfSquares
= __SMLALD(in
, in
, sumOfSquares
);
106 in
= *__SIMD32(pSrc
)++;
107 sum
+= ((in
<< 16) >> 16);
109 sumOfSquares
= __SMLALD(in
, in
, sumOfSquares
);
111 /* Decrement the loop counter */
115 /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
116 ** No loop unrolling is used. */
117 blkCnt
= blockSize
% 0x4u
;
121 /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
122 /* Compute Sum of squares of the input samples
123 * and then store the result in a temporary variable, sum. */
125 sumOfSquares
= __SMLALD(in1
, in1
, sumOfSquares
);
128 /* Decrement the loop counter */
132 /* Compute Mean of squares of the input samples
133 * and then store the result in a temporary variable, meanOfSquares. */
134 t
= (q15_t
) ((1.0 / (blockSize
- 1)) * 16384LL);
135 sumOfSquares
= __SSAT((sumOfSquares
>> 15u), 16u);
137 meanOfSquares
= (q31_t
) ((sumOfSquares
* t
) >> 14u);
139 /* Compute mean of all input values */
140 t
= (q15_t
) ((1.0 / (blockSize
* (blockSize
- 1))) * 32768LL);
141 mean
= (q15_t
) __SSAT(sum
, 16u);
143 /* Compute square of mean */
144 squareOfMean
= ((q31_t
) mean
* mean
) >> 15;
145 squareOfMean
= (q31_t
) (((q63_t
) squareOfMean
* t
) >> 15);
147 /* mean of the squares minus the square of the mean. */
148 in1
= (q15_t
) (meanOfSquares
- squareOfMean
);
150 /* Compute standard deviation and store the result to the destination */
151 arm_sqrt_q15(in1
, pResult
);
155 /* Run the below code for Cortex-M0 */
156 q15_t in
; /* input value */
158 /* Loop over blockSize number of values */
163 /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
164 /* Compute Sum of squares of the input samples
165 * and then store the result in a temporary variable, sumOfSquares. */
167 sumOfSquares
+= (in
* in
);
169 /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
170 /* Compute sum of all input values and then store the result in a temporary variable, sum. */
173 /* Decrement the loop counter */
177 /* Compute Mean of squares of the input samples
178 * and then store the result in a temporary variable, meanOfSquares. */
179 t
= (q15_t
) ((1.0 / (blockSize
- 1)) * 16384LL);
180 sumOfSquares
= __SSAT((sumOfSquares
>> 15u), 16u);
181 meanOfSquares
= (q31_t
) ((sumOfSquares
* t
) >> 14u);
183 /* Compute mean of all input values */
184 mean
= (q15_t
) __SSAT(sum
, 16u);
186 /* Compute square of mean of the input samples
187 * and then store the result in a temporary variable, squareOfMean.*/
188 t
= (q15_t
) ((1.0 / (blockSize
* (blockSize
- 1))) * 32768LL);
189 squareOfMean
= ((q31_t
) mean
* mean
) >> 15;
190 squareOfMean
= (q31_t
) (((q63_t
) squareOfMean
* t
) >> 15);
192 /* mean of the squares minus the square of the mean. */
193 in
= (q15_t
) (meanOfSquares
- squareOfMean
);
195 /* Compute standard deviation and store the result to the destination */
196 arm_sqrt_q15(in
, pResult
);
198 #endif /* #ifndef ARM_MATH_CM0_FAMILY */
204 * @} end of STD group